There was a bug in how MapWindow was calculating the numpy array slices
when drawing the map. Redo how this works so that MapWindow can draw
maps of arbitrary size and center maps that are smaller than the window's
drawable area.
- Move all map rendering to a new MapWindow class
- Clip map rendering to the bounds of the Window
- Pass in Entities list from the Engine and render them relative to the window
The map doesn't scroll yet, so it'll always be clipped on the bottom and
right.
